Identifiable polyamide fibers containing lead acetate



tying agent.

United States Patent ()fiice 3,066,034 Patented Nov. 27, 1962 3,066,034 IDENTIFIABLE POLYAMIDE FIBERS CONTAINING LEAD ACETATE Samuel C. Temin, Borough of Churchill, Allegheny County, Pa., assignor, by mesne assignments, to Midling-gloss Corporation, Cleveland, Ohio, a corporation No Drawing. Filed Apr. 6, 1959, Ser. No. 804,123 8 Claims. (Cl. 106-494) This invention relates to the manufacture of shaped articles of organic polymeric material which include an identi- More specifically, this invention relates to linear synthetic polyamide fibers, filaments, and other shaped articles which have combined with them a relatively small amount of lead whereby the article may be readily identified.

For many purposes, it is desirable to be able to identify a manufactured organic polymeric or plastic product as to its origin of manufacture, the nature of the material and the method of preparation. Frequently, manufacturers of articles which take a standard shape or configuration regardless of origin wish to distinguish their articles or particular lots of their articles from those of other manufacturers. Filamentary articles such as, fibers, filaments, yarns, cords, tows, and the like are examples of such standard shaped articles and this invention will be described with respect to such filamentary articles, although i-ts scope is not intended to be so limited. The most readily accomplished means for distinguishing such articles is by the addition of some foreign substance that imparts an identifiable characteristic to the article such as color, a characteristic flame or chemical test, and the like. The prime requisite of a suitable foreign substance is that it be readily identifiable by some simple test. Other considerations, however, are also important such as its ease of application and the permanence of its retention on the article. Also, the appearance of many products is critical to their usefulness so that the foreign substance added must not alter the appearance or processability of the article.

It has been proposed to treat strands of yarn and the like with insoluble metallic elements and compounds for the purpose of subsequent identification. Many of these materials are readily identified by a characteristic flame test but due to the essential insoluble nature of these substances in the common solvents the application of such materials to yarn has proved difiicult. Also, some of the materials suggested, such as silicates or oxides of the elements beryllium, zirconium and bismuth, among others, are diificult to detect unless extensive laboratory equipment is available. These materials, of course, can be detected by spectrographic analysis but there is no means of detecting their presence in the field where identification of the article is most frequently desired.

It has also been proposed to apply to filaments and fibers and fibers salts such as nickel and strontium chloride which are water soluble and, therefore, easily applied in aqueous solution. However, since these compounds are soluble in water, subsequent treatment of the fiber by many of the common textile processes which use aqueous solutions result in the compound being substantially removed. Also, if fibers containing these compounds are scoured or dyed with other yarns, there is the possibility that the compounds will bleed into the solutions and be deposited on the other yarns. This, of course, nullifies the selectivity of their identification of a particular fiber.

In some industrial applications for fibers, it is common to identify the yarns by using distinctive coloring. This method of identification is naturally limited to those applications in which the fibers appearance is not significant in its use or apparent to the consumer such as when it is used as a reinforcing material in rubber or the like. The use of this means of identification is also handicapped by the fact that colors are very difficult to standardize from one dye lot to the next. It is possible that more than one manufacturer may use comparable colors which would result in confusion not only with the same manufacturers products but ,also with other manufacturers products.

Now a means has been found for preparing a fiber for subsequent identification which is readily detectable in the field, substantially permanent, and yet easily executed. Furthermore, the inclusion of the identifying agent of this invention in or on a fiber does not alter the appearance of the fiber or result in undesirable changes occurring during subsequent processes normally employed in the textile art.

In accordance with this invention, a relatively small amount of lead is included in or applied on a shaped article composed of an organic polymeric material. Advantageously, the lead may be incorporated in a linear synthetic polyamide material, which term as used herein is defined to mean any long chain synthetic polyamide material which has recurring amide groups as an integral part of the main polymer chain and which is capable of being formed into a filament in which the structural elements are oriented in the direction of the axis, prior to its extrusion, moulding, or casting or it may be applied to the shaped article by spraying, dipping, or padding in the form of an aqueous solution of lead acetate.

This means can be used in identifying shaped articles made of any organic polymeric material but particular advantages have been found in its use with a fiber-forming polymer selected from the group consisting of linear synthetic polyamides, regenerated celluloses, polyacrylonitriles, polyesters, polyolefines, and cellulose esters. Although this means of identification may be used with any of these organic polymeric materials, it has been found particularly well adapted for identifying shaped articles comprised of linear synthetic polyamide materials. Examples of usable linear synthetic polyamides are those selected from the group consisting of polyhexamethylenediamine adipate and polycaprolactam. Shaped articles comprised of polyhexamethylenediamine adipate, or nylon 66, are prepared by first polymerizing the salt produced from the reaction of equal portions of hexamethylenediamine and adipic acid. This polymer is subsequently melt extruded into a film which is solidified and the solid film broken into chips to facilitate remelting, filtering and spinning or forming into the desired shaped article. Although polyhexamethylenediamine adipate is the most commonly used polymer of this type, other diamine and dibasic acids produce salts suitable for polymerizing and shaping into useful articles which may be identified by the addition of lead. Shaped articles of polycaprolactam, or nylon 6, are prepared by the polymerization of the lactam of e-aminocaproic acid, generally referred to as u,e-caprolactam or just caprolactam. This polymerization is accomplished by heating the lactam in the presence of a catalyst, such as water, which causes the lactam ring to open and form a linear polymeric product. The linear polymeric amide can either be melt spun directly into fibers or other shaped articles or formed into chips that may be washed prior to being remelted and formed or spun into shaped articles. In the formation of either of these types of linear synthetic polyamide materials, the lead may be added in suitable form to the melt during polymerization, the chips prior to remelting, or the completed shaped article. When the lead is added during polymerization, such as by incorporation in the diamine or acid reactant or in the catalyst for the lactam polymerization, it is uniformly distributed throughout the chips and, hence, the completed article. Similarly, when the lead is applied to the chips it appears as a more or less homogeneous dispersion in the subsequent shaped article. Application of the lead to the finished shaped article, of course, results in it being present only on the surface of the article. This means of addition is somewhat more fiexible and less time consuming than those suggested above and yet it is equally effective in providing permanent identification.

Ease of application or addition of the lead to the polymeric materials is a principal concern in providing an economical means of identification and one of universal utility. Application by means of an aqueous solution readily lend itself to the textile industry, particularly since yarns and fabrics are commonly treated by spraying, dipping, or padding in aqueous solutions. There are a number of lead compounds which exhibit water solubility and, hence, are suitable as identifying agents but particular advantages have been found in the use of lead acetate. Surprisingly, even when lead acetate is applied to the surface of a finished article, as distinguished from being incorporated in the article during the polymerization or rernclting steps, the lead acetate is not readily washed off of the yarn by the various solutions used in scouring, dyeing, sizing and finishing fibers, filaments, films and the like.

Furthermore, the usual washing and dry-cleaning olutions and solvents employed on textile fabrics formed from such fibers do not remove the lead nor cause it to bleed onto another fiber not originally so treated when washed or dry-cleaned in the same solution.

Frequently, it is necessary or desirable to identify yarn at a location where large laboratory facilities are not available or under condition which do not warrant the expense of extensive and complicated testing. Advantageously, lead when added in accordance with this invention may be easily and quickly identified by the dithizone test using the following reagents:

(a) 1% nitric acid solution.

(b) Buffer solution (250 ml. of ammonium hydroxide, 1 gm. of sodium sulphite, and 1 gm. of potassium cyanide in 450 ml. of distilled water).

(c) Dithizone solution (30 mg. diphenylthiocarbozone dissolved in 500 ml. of chloroform).

The procedure in making the dithizone test requires a minimum of equipment and skill upon the part of the person carrying it out. In this respect, the proportions specified below are not highly critical although it is recommended that they be adhered to as closely as practicable in order to insure valid results. The only critical requirement for good results is that the dithizone solution has a purity of at least about 90% and preferably a purity of 93% or better.

. DITHIZONE TEST A 1 gm. sample of the article to be tested is placed in a test tube and ml. of the nitric acid solution are added. This solution is heated and 30 cc. of the buffer solution are introduced with vigorous mixing for 25 to 30 seconds. Then 10 ml. of the dithizone solution are added and the test tube isagainvigorously agitated. The solution is allowed to settle and in a very short time a bright red color appears at the bottom of the test tube indicating the presence of lead. If no red color appears, the test is negative indicating the absence of lead.

It is, of course, recognized that in determining the presence of lead, other testing methods may be used such as, for example, spectrographic analysis, and other chemical means and it is, therefore, not the intention of the inventor to be limited to but one method of testing. All of the other methods of testing, however, involve either extensive laboratory equipment or complicated procedures requiring highly skilled technicians. In contrast, the dithizone test provides a means of easily, simply, quickly, and accurately confirming the presence of lead in organic polymeric materials and i thus advantageously employed in conjunction with this invention.

Advantageously, it has been found that positive results are obtained by the dithizone test when a relatively small amount of lead is present in the polymeric material. It is, of course, desirable to maintain the concentration of lead as low as possible in order to minimize the possibility of its adversely affecting the properties or appearance of the finished yarn. However, at least about 0.0035% by weight of lead based on the weight of the article must be present to assure accurate test results. Although the lead may be added advantageously in the form of lead acetate it may react during or after addition such as by oxidation and be present in a wholly different form. It may be that it reacts in some way with the polymeric material which would account for the remarkable tenacity with which it is retained even through subsequent treatments. Such considerations are, however, theoretical and this invention is not intended to be limited thereby since regardless of .the form in which it is added or the form it may subsequently take, concentrations of lead between about 0.0035 and 0.05% by weight on the weight of the finished article have shown particular advantages in assuring positive test results without altering the quality of the article in which it is incorporated.

In the preparation of fibers, filaments, and films from organic polymeric materials and particularly linear synthetic polyamide materials, it is frequently desirable to incorporate other additives, such as delusterants, pigments, viscosity stabilizers and the like, or to subsequently treat the completed or partially completed articles by dyeing or finishing. In this regard, it has been suggested as advantageous that an antioxidant and light stabilizer material be added to linear synthetic polyamide articles which have been delustered with titanium dioxide. Advantageously, the incorporation of lead acetate with such materials and the after-treatments described above are not affected by the presence of lead in the amounts of this invention as to their eifectiveness or the appearance and quality of the complete article made therefrom.

This invention now will be more fully described by the following examples although it is understood that the invention is not to be limited by these examples. In these examples, parts and percent of materials are intended to mean parts and percent by weight.

Example I Lead in the form of lead acetate is thoroughly dispersed in polycaprolactam fibers by its addition to the catalyst during polymerization in the following way:

In .the polymerization of e-caprolactam, a catalyst solution comprised of 7 parts of monomeric e-caprolactam, 5 parts of water, and 0.02 part of lead acetate are heated with 400 parts of e-caprolactam to a temperature of 250i5 C. At the end of about 56 hours the polymerizate has attained a relative viscosity of about 2.46 and is spun directly into a substantially undrawn yarn of 1850 denier and 70 filaments. The undrawn yarn is doubled and then drawn about 5.12 times its original length resulting in a 798 denier yarn having a tenacity of 5.98 gms./denier and an elongation not exceeding about 15.0%. The pres once of the lead in no way interferes with the uniformity of the yarn and, hence, its continuity of drawing. Furthermore, the yarn is perfectly white and in all respects its properties, processing, and qualities are the same as yarn similarly spun in the absence of lead.

A representative sample of the yarn is then acidified and buffered in accordance with the dithizonetest procedure described above and the dithizone solution added. A distinctly red coloration appears indicating a positive reaction for the presence of lead.

A yarn is prepared in the same manner as that described above except for the inclusion of lead acetate in the catalyst solution. This yarn, when treated in accordance with the dithizone test procedure, resulted in no red coloration being observed and, thus, is clearly distinguished from the yarn containing lead.

Example 11 In the production of viscose rayon by the process wellknown in the art wherein cellulose wood pulp is steeped, shredded, aged, xanthated, and then dissolved, a 0.3% aqueous solution of lead acetate is added to the viscose mix during the dissolving step to the extent of 0. 0075 by weight of lead on the weight of the cellulose. The viscose is ripened and spun into an aqueous acid spin bath containing about 9% sulfuric acid, 22.5% sodium sulfate, and 3% Zinc sulfate to produce a 150 denier, 30 filament yarn. The yarn is washed, bleached, oiled, dried and collected on a bobbin.

A sample of the yarn is then treated in accordance with the dithizone test as described above and exhibits a definite red coloration indicating the presence of lead. The test is carried out easily and quickly and gives an unmistakable positive result indicating the fact that the yarn has lead present in an amount greater than what might have been occluded on it as a contaminant. Moreover, the incorporation of the lead in the viscose does not adversely affect its spinning or processing nor does it in any way discolor the finished yarn or impair its quality. For all intents and purposes the yarn exhibits comparable properties to a yarn similarly produced but without the addition of lead acetate.

Example III A solution of 4.2 parts lead acetate in 150 parts of water are sprayed on 9000 parts of polyhexamethylenediamine adipate chips prepared by the polymerization of the reaction product of hexamethylenediamine and adipic acid in the manner well-known in the art. The treated chips are dried and charged into a melt spinning apparatus, such as that shown in US. Patent No. 2,253,176, and spun into a yarn of approximately 4200 denier and 140 filaments. This yarn is then drawn about 5.0 times to increase its tenacity to 8.2 grams per denier. The yarn is spun normally and drawn continuously without excessive filamentation or breaks to produce a white yarn of good quality.

A sample of the yarn is then tested in a buffered acidic solution with dithizone solution in the manner described above. A positive and unmistakable test for lead is obtained.

Example IV In order to determine the permanency of the lead in or on the yarn, samples of each of the yarns produced with lead acetate by the methods described in Examples I and III are scoured along with similar yarns without lead. A sample of lead-containing yarn and non lead-containing yarn are boiled together for one hour in each of the following aqueous solutions:

( 1) A non-ionic allylarylpolyether alcohol detergent solution, such as Triton NE marketed by Rohm & Haas Company (neutral solution).

(2) Tri-sodium phosphate solution (alkaline solution).

(3) 5% acetic acid solution (acidic solution).

Each of the yarns is then tested by the dithizone method and in every case the yarn previously known to contain lead gives a positive result while those known to have been produced without lead acetate show no red coloration. Furthermore, the three solutions were also tested and gave negative results indicating there was not sulficient, if any, lead washed out of the yarn to be detected.

Example V The effect of subsequent dyeing of the yarn when lead is present in the concentrations necessary for identification is tested by dyeing samples of yarn produced with lead acetate as described in Examples I and III. The yarns are dyed with a 0.1% acid metallized dye having a New Color Index number of Acid Red 212, such as Neolan Red BRE marketed by Ciba Company and then half of the sample of each type of yarn is stripped of the dye.

Both the dyed and dye-stripped samples of yarn are then tested with the prescribed dithizone test and give positive results. Further, the dye bath and stripping bath are tested and give negative results. This test indicates that the identification of a yarn by the inclusion of lead is not interfered with by dyeing nor is it rendered ineffective by subsequent stripping of the dye. Moreover, the lead does not leach out into the dye bath and, thus, possibly contaminate other fibers sought to be dyed in the same bath.

Example Vl If the lead added in or on the shaped article, in this. case fibers, should discolor the product initially or during subsequent use, it would be of limited value as an identifying agent. Previous examples have shown that it does not discolor the fibers initially and the following exposure tests indicate that subsequent discoloration, also, does not occur in the concentrations of lead of this invention.

Four samples of yarn produced with the inclusion of lead acetate as described in Example I are exposed for seven days to the following materials:

(1) Ammonium hydroxide-hydrogen sulfide solution (2) Acetic acid (0.5 %)-hydrogen sulfide solution (3) Carbon disulfide solution (4) Sulfur precipitate powder At the conclusion of the period, the exposed yarn samples are examined and found not to be discolored, having maintained substantially the same whiteness as the fibers not so exposed. When the yarn samples are tested by the dithizone test they still indicate a positive presence of lead. Yarns having concentrations of lead up to about 0.05% when similarly exposed advantageously do not indicate any discoloration. However, when the lead concentration exceeds about 500 parts per million slight discolorations begin to appear.

Frequently yarns are produced from organic polymeric materials with various foreign substances added to obtain specific desirable characteristics such as, for example, delusterants, pigments, antioxidants, light stabilizers and the like. In many cases, the yarn may contain more than one of these materials in order to provide the benefits of each or the synergistic benefits of the additives in combination. The most commonly used delusterant in polyamide fibers is titanium dioxide. It is believed, however, that the presence of titanium dioxide promotes degradation of the polymer when it is exposed to light and so it very frequently appears in the polymer with a light stabilizer compound such as a member selected from the group consisting of substituted Z-hydroxybenzophenones, salicylic acid derivatives, benzotriazole derivatives, and inorganic chromium and manganese compounds. Particular advantages have been found in using light stabilizers of ultra-violet light absorbers such as the substituted 2 hydroxybenzophenones, 2 hydroxy-4-methoxybenzophenone, 2,2-dihydroxy-4-methoxybenzophenone, and

U 2,2-dihydroxy-4,4dimethoxybenzophenone. Also, such salicylic acid derivatives as phenyl salicylate and 4-t-butyl phenyl salicylate have been found to be advantageously utilizable as have such inorganic compounds as manganese oxalate, manganese hyposulfite and chromium fluoride. Advantageously, the presence of lead when added in the form of lead acetate in accordance with this invention does not interfere with the properties secured by the use of these various additives. Conversely, the presence of these additives does not impair the ready identification of objects containing lead in the concentrations of this invention. It has been found that somewhat greater advantages result from using a relatively small amount of a light stabilizer compound such as those mentioned above along with the lead in preparing polyamide fibers for identification. The combination of lead and a light stabilizer in or on a polyamide fiber provides a fiber of enhanced light stability, good whiteness, easy processability, and with the additional feature of being readily identified by a simple and reliable means.

Since certain changes in the practice of this invention may be readily made without substantially departing from its spirit or Scope, it is to be understood that all the foregoing be interpreted as being merely illustrative and is not to be construed as limiting or restricting the invention as particularly pointed out and defined in the appended claims.

What is claimed is:

1. As an article of manufacture, a shaped article comprising a fiber forming organic polymeric material selected from the group consisting of linear synthetic polyamide, regenerated cellulose, polyacrylonitrile, polyester, polyolefin, and cellulose ester and between about 0.0035% and 0.05 on the weight of said fiber forming organic polymeric material, of lead acetate.

2. As an article of manufacture, a filamentary article comprising a linear synthetic polyamide and between about 0.0035% and 0.05% of lead acetate on the weight of the linear synthetic polyamide.

3. As an article of manufacture, a filamentary article comprising the product of a linear synthetic polyamide and at least about 0.0035 on the weight of said synthetic linear polycarbonamide, of lead acetate mixed while said linear synthetic polyamide polycarbonamide is in the melt state.

4. As an article of manufacture, a filamentary article comprising a linear synthetic polyamide having between about 0.0035 and 0.05% of lead acetate on the weight of the linear synthetic polyamide and a relatively small amount of a light stabilizer compound.

5. An article of manufacture as defined in claim 4 wherein the light stabilizer compound is a member selected from the group consisting of substituted 2-hydroxybenzophenones, salicylic acid derivatives, benzotriazole derivatives, and inorganic chromium and manganese compounds.

6. In a process for the production of shaped articles of fiber forming organic polymeric material whereby the shaped articles are rendered readily identifiable the step consisting essentially of adding between about 0.0035% and 0.05 on the weight of said fiber forming organic polymeric material, of lead to the shaped articles in the form of an aqueous lead acetate solution.

7. A process for the production of filamentary articles of fiber-forming polymer wherein the filamentary articles are rendered readily identifiable comprising incorporating in the fiber-forming polymer prior to extrusion at least about 0.0035 on the weight of said fiber forming polymer, of lead acetate and spinning the lead containing fiber-forming polymer into filamentary articles.

8. A process for the production of filamentary articles of linear synthetic polyamide wherein the filamentary articles are rendered readily identifiable comprising treating linear synthetic polyamide chips with an aqueous lead acetate solution, melting said treated chips, and spinning the melt of said treated chips into filamentary articles.

References Cited in the file of this patent UNITED STATES PATENTS 2,265,473 Cannell Dec. 9, 1941 2,324,101 McMahon July 13, 1943 2,390,512 Collins Dec. 11, 1945 2,637,657 Ozols May 5, 1953 2,662,822 Land Dec. 15, 1953 2,695,425 Stott Nov. 30, 1954 2,748,099 Bruner et al May 20, 1956 2,753,272 Collins July 3, 1956 2,824,080 Haux d. Feb. 18, 1958 2,851,370 Blank Sept. 9, 1958 OTHER REFERENCES Polyamide Resins, by D. Floyd, Reinhold Pub. Corp, NY. (1958), page 1. 

1. AS AN ARTICLE OF MANUFACTURE, SHAPED ARTICLE COMPRISING A FIBER FORMING ORGANIC POLYMERIC MATERIAL SELECTED FROM THE GROUP CONSISTING OF LINEAR SYNETHETIC POLYAMIDE, REGENARATED CELLULOSE, POLYACRYLONITRILE, POLYESTER, POLYOLEFIN, AND CELLULOSE ESTER AND BETWEEN ABOUT 0.0035% AND 0.05%, ON THE WEIGHT OF SAID FIBER FORMING ORGANIC POLYMERIC MATERIAL, OF LEAD ACETATE. 